The Underappreciated Villain Role
When concerning yourselves with the characters that drive a plot, many people will mistakenly label heroes as the most important. They're the ones that do stuff. They save the day, get the recognition, and drive much of the plot with their efforts. It's perfectly natural to value a hero. They're usually the ones we follow in a story. Even minor characters play their own little role in the grand scheme of the plot and, as a result, even they can overshadow a villain from time to time. This is a mistaken sentiment on the part of the casual reader, watcher, and gamer. They can despise a villain all they want, but when you think about it, the villain is actually rather important. Imagine the hero from your favorite story. Now imagine what that hero would be doing if the villain wasn't around. Hm? Exactly. The hero would be doing nothing.
The subtle relationship between the hero and villain is almost always a simple case of cause and effect. The villain is the catalyst for the plot. He can be a malevolent ruler against whom the hero rebels, or a monstrous criminal (or... thing) that does evil stuff. The hero's role in this case is reactionary. He either seeks revenge against the villain or seeks to undo what the villain is doing. I mean, let's be honest. Can anyone honestly say they would watch a story without the conflict generated by a bad guy?
In addition to effectively giving the plot life, a well-written villain can also have another important effect on the story. This isn't as important to the plot, but it makes it more entertaining: they can change a hero. Perhaps the hero's morals become more relaxed, or they become more serious or mopey. Sometimes, the whole personality of a hero can be overhauled based on their encounter with the big bad. For example, a lot of Joss Whedon's work comes to mind. The main character of Firefly, Malcolm Reynolds, was once a charismatic leader with a strong faith and powerful optimism. Upon losing a war with the antagonistic Alliance, he would renounce his faith, and ultimately become much more cynical and violent. While, I do not minimize his sufferings, these radical changes give him much more depth than the cheery soldier who believed God to be on his side. And in the world of Buffy the Vampire Slayer, the heroine became slightly more mature following the evil-turn of Angel. A slightly less ditzy Buffy is little else but an improvement. In other cases, it is the villain who makes the hero, as is the case in the fantasy novel, Eragon. How did the farm boy who previously posed no threat to the evil emperor become the champion of the rebellion against him? He hunted dragons, causing the hurried escape with the egg of the dragon that would eventually become Eragon's companion. And what's more? He slew Eragon's family over the whereabouts of that egg, thus forcing him from his uneventful lifestyle into the very thing the evil king feared.
Now, this isn't to say that a story necessarily needs a villain to create the conflict necessary for a story to be entertaining. Some can utilize internal conflict as well. But, to understand this type of conflict, you have to understand what the conflict is. For example, let's take a story in which a main character obsesses over a difficult decision. The situation exists because there are consequences to each side that are less than ideal. What creates these consequences? More importantly, what is the cause for the situation being made in the first place? It is no villain that is the cause of such plots usually, however these are frequently caused by some form of antagonism that makes the decision necessary. Even if it is a question of preference, the internal battle makes the character into his or her own antagonist. I like to call this self-inflicted antagonism.
Without being too philosophical, I believe that even in ourselves, there is a villain waiting to oppose us when no one else will. This establishes the villain as the most important character in a story, save the protagonist. He sets the stage for the hero's actions, often giving him something to do in the first place.